TWI706588B - Anode structure with binders for silicon and stabilized lithium metal powder - Google Patents

Abstract

A simple solution processing method is developed to achieve uniform and scalable stabilized lithium metal powder coating on Li-ion negative electrode. A solvent and binder system for stabilized lithium metal powder coating is developed, including the selection of solvent, polymer binder and enhancement of polymer concentration. The enhanced binder solution is 1% concentration of polymer binder in xylene, and the polymer binder is chosen as the mixture of poly(styrene-co-butadiene) rubber (SBR) and polystyrene (PS). Long-sustained, uniformly dispersed stabilized lithium metal powder suspension can be achieved with the enhanced binder solution. A uniform stabilized lithium metal powder coating can be achieved with simple doctor blade coating method and the resulting stabilized lithium metal powder coating can firmly glued on the anode surface. With the prelithiation of negative electrode by stabilized lithium metal powder, improvements in electrochemical performances are demonstrated in both graphite/NMC and SiO/NMC full-cell.

Description

Anode structure with binder for silicon and stabilized lithium metal powder

The embodiment of the present invention relates to high-capacity energy storage devices and energy storage device components, and more particularly to the use of processes incorporating stabilized lithium metal powder (such as "SLMP") to manufacture high-capacity energy storage devices and energy storage devices. Composition and method of device components.

A lithium ion battery is a rechargeable battery in which lithium ions move between negative and positive electrodes. Lithium ions move from the negative electrode to the positive electrode via the electrolyte during discharge, and move backward from the positive electrode to the negative electrode during charging. Most commonly, the negative electrode is made of graphite. Since graphite forms a solid electrolyte interface (SEI) layer with little volume change, it is stable during charge and discharge cycles, so graphite is particularly preferred.

Currently, lithium (Li)-ion battery technology is facing increasing demands for higher energy density and higher power output for portable electronic devices and electric vehicle applications. To improve the performance of lithium-ion batteries. The next generation of lithium-ion batteries with high-energy density alloy anode materials (such as silicon, germanium, and tin) has received high attention. The limitation of these materials is high irreversible capacity loss (20%-40%, depending on the battery chemistry), which will result in low coulombic efficiency (CE) in the initial cycle.

When striving to design high-power batteries, reducing the particle size of the active material to the nanometer size will help shorten the diffusion length of charged carriers and enhance the lithium ion diffusion coefficient, thus achieving faster reaction power. However, the use of nano-scale active material particles generally results in a higher first cycle irreversible capacity loss, which is caused by the formation of a larger reaction area at the solid electrolyte interface (SEI). Many attempts have been proposed to compensate for this capacity inefficiency, such as excessive cathode material loading, increased lithium salt concentration, lithium sacrificial salt, lithium-rich cathode material, and application of stabilized lithium metal powder (SLMP). However, there is still a need for high-energy storage devices and improved methods for forming high-energy storage devices.

The embodiment of the present invention relates to high-capacity energy storage devices and energy storage device components, and more particularly relates to the use of a process incorporating stabilized lithium metal powder (SLMP) to manufacture such high-capacity energy storage devices and energy storage device components The composition and method. In one embodiment, a method of fabricating an electrode structure is provided. The method includes forming a hydrocarbon solvent, a binder solution of styrene-butadiene rubber (SBR) and polystyrene (PS), adding stabilized lithium metal powder (SLMP) to the binder solution to form a slurry, and deposit a slurry The film is placed on the substrate, and the film and the substrate are exposed to a drying process to form an electrode structure.

In another embodiment, a method of forming a stabilized lithium metal powder (SLMP) suspension is provided. The method includes dissolving styrene-butadiene rubber (SBR) and polystyrene (PS) in xylene to form a bond Agent solution, and adding SLMP to the binder solution to form a SLMP suspension.

In yet another embodiment, a method of forming a battery is provided. The method includes forming an electrode structure. The electrode structure is formed by forming a hydrocarbon solvent, a binder solution of styrene-butadiene rubber (SBR) and polystyrene (PS), and adding stabilized lithium metal powder (SLMP) to the binder solution to form a slurry , Depositing the slurry film on the substrate, and exposing the film and the substrate to a drying process to form an electrode structure. The method further includes combining the electrode structure with the positive electrode structure, a first current collector contacting the positive electrode structure, a second current collector contacting the electrode structure, and a separator disposed between the positive electrode structure and the negative electrode structure.

The method of stabilizing lithium metal powder (SLMP) and forming an electrode containing SLMP is described below. Certain details are described below and in Figures 1 to 4 to thoroughly understand various embodiments of the present invention. In the following, other known structures and system description details generally related to electrode formation and SLMP are not described, so as not to unnecessarily obscure the description of various embodiments.

Many of the details, dimensions, angles and other features shown in the figures are only examples of specific embodiments. Therefore, other embodiments may have other details, components, dimensions, angles, and characteristic structures without departing from the spirit or scope of the present invention. In addition, other embodiments of the present invention may not be practiced according to the following details.

SLMP is generally lithium metal particles coated with a thin lithium salt layer (such as Li ₂ CO ₃ ). This thin lithium salt protective coating can dispose of SLMP in the dry room atmosphere, so it can greatly expand the usage of SLMP. SLMP usually has a very high capacity of 3600 milliampere hour/gram (mAhg ^-1 ), and can effectively compensate for the first cycle capacity loss through prelithiation. In addition, SLMP has several attractive uses. First, SLMP can pre-lithiate anode electrodes, especially alloy anodes or nano-level anodes, to compensate for the lithium loss of the cathode during the formation of SEI, and achieve high energy density and high power density batteries. Second, SLMP pre-lithiation can replace the charge formation process in lithium-ion battery manufacturing. It is known that the charge formation process is essential to form a good SEI layer, and the SEI layer is the key to battery performance. However, the charge formation process is an energy-consuming and time-consuming process. The high-quality SEI layer can be formed during the SLMP prelithiation process, in which only SLMP loading, activation and 48 hours of rest are required. Third, SLMP can be used as an independent lithium source for some non-lithiation cathode materials with high specific capacity, such as reduced graphene oxide/Fe ₂ O ₃ composite, V ₆ O ₁₃ , MnO ₂ and metal fluorides, such as BiF ₃ . These non-lithiated cathode materials provide cathodes for non-lithium, and when coupled to the SLMP pre-lithiated anode of a lithium ion device, some will exhibit high weight and volume energy density.

Although SLMP has proven to be cost-effective in the application of lithium-ion devices; disposal and application of SLMP on the anode surface is still challenging. The lithium salt protective layer on the surface of the SLMP needs to be destroyed to expose the lithium metal and make electrical contact between the lithium and the anode to achieve SLMP prelithiation. Therefore, the feasibility of pressurized activation of SLMP should also be considered. The effective activation of SLMP was previously studied, and high first-cycle Coulombic efficiency and excellent long-term cycle performance can be achieved in graphite/NMC full cells. However, the research needs of SLMP are not limited to studying the mechanism of SLMP and the possible application of pre-lithiation, but can also be applied to achieve safer, cheaper and scalable processes for lithium-ion devices. The spray method of SLMP coating generally uses surfactants to improve the dispersion of SLMP. Surfactants may cause inappropriate side reactions.

In some embodiments of the present invention, a solution process slot die coating method is provided to achieve a uniform and expandable SLMP coating on the anode surface. In some embodiments, the polymer binder is introduced into the coating solution to assist and maintain the uniform dispersion of the SLMP during the long-term processing time, and act as a binder to fix the SLMP on the anode surface. With the above embodiments, a controllable uniform SLMP coating can be formed on the electrode surface. These SLMP coatings can be easily activated by applying calendering pressure. The SLMP pre-lithiation effect achieved by some embodiments of the present invention can be confirmed by the electrochemical performance of graphite/NMC and SiO/NMC full cells.

Figure 1 illustrates an example of a Li-ion battery structure 100 having a negative electrode structure 140 formed according to an embodiment of the present invention. The Li ion battery structure 100 has a positive current collector 110, a positive electrode structure 120, a separator 130, a negative electrode structure 140, and a negative current collector 150. Note that the current collector shown in Figure 1 extends beyond the stack, but the current collector does not necessarily extend beyond the stack. The part that extends beyond the stack can be used as an ear piece.

The current collectors 110 and 150 of the positive electrode structure 120 and the negative electrode structure 140 may be the same or different electronic conductors. Examples of metals that the current collectors 110 and 150 may contain include aluminum (Al), copper (Cu), zinc (Zn), nickel (Ni), cobalt (Co), tin (Sn), silicon (Si), manganese (Mn) , Magnesium (Mg), the above alloy and the above composition. In one embodiment, at least one current collector 110, 150 is perforated. In addition, the current collector can have any form factor (such as metal foil, sheet, or plate), shape, and microporous/macroporous structure. Generally, in a square battery, the tabs are formed of the same material as the current collector, and can be formed during the manufacturing stack or added later. All parts except the current collectors 110 and 150 contain lithium ion electrolyte.

The negative electrode structure 140 or the anode is formed according to the described embodiment. The energy capacity of the negative electrode structure 140 may be greater than or equal to 372 milliampere hour/gram (mAh/g), preferably ³700 mAh/g, and most preferably ³1000 mAh/g. The negative electrode structure 140 may include carbon (for example, coke, graphite), silicon (for example, silicon oxide), or the foregoing combination. The negative electrode structure 140 may further include materials such as lithium, nickel, copper, tin, indium, the foregoing oxides, or the foregoing combinations. According to one or more embodiments described, the negative electrode structure 140 is coated with a film containing SLMP.

The positive electrode structure 120 or the cathode may be any material compatible with the anode, and may include intercalation compounds, intercalation compounds, or electrochemically activated polymers. Suitable intercalation materials include, for example, lithium-containing metal oxides, MoS ₂ , FeS ₂ , MnO ₂ , TiS ₂ , NbSe ₃ , LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , V ₆ O ₁₃ , V ₂ O _5. BiF ₃ and Fe ₂ O ₃ . Suitable polymers include, for example, polyacetylene, polypyrrole, polyaniline, and polythiophene. The positive electrode structure 120 or the cathode may be made of layered oxide (for example, lithium cobalt oxide), olivine (for example, lithium iron phosphate), or spinel (for example, lithium manganese oxide). Exemplary lithium-containing oxides may be layered (such as lithium cobalt oxide (LiCoO ₂ )) or mixed metal oxides, such as LiNi _x Co _1-2x MnO ₂ , LiNiMnCoO ₂ (NMC), LiNi _0.5 Mn _1.5 O ₄ , Li (Ni _0.8 Co _0.15 Al _0.05 )O ₂ , LiMn ₂ O ₄ , and doped lithium-rich layered-layered materials, where x is a zero or non-zero number. Exemplary phosphates may be iron olivine (LiFePO ₄ ) and variants (eg LiFe _(1-x) Mg _x PO ₄ ), LiMoPO ₄ , LiCoPO ₄ , LiNiPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , LiVOPO _4. LiMP ₂ O ₇ or LiFe _1.5 P ₂ O ₇ , where x is a zero or non-zero number. Exemplary fluorophosphates may be LiVPO ₄ F, LiAlPO ₄ F, Li ₅ V(PO ₄ ) ₂ F ₂ , Li ₅ Cr(PO ₄ ) ₂ F ₂ , Li ₂ CoPO ₄ F, or Li ₂ NiPO ₄ F. Exemplary silicates may be Li ₂ FeSiO ₄ , Li ₂ MnSiO ₄ or Li ₂ VOSiO ₄ . An exemplary non-lithium compound is Na ₅ V ₂ (PO ₄ ) ₂ F ₃ .

In some embodiments of the present invention, lithium is contained in the atomic layer of carbon graphite (LiC ₆ ) crystal structure of the negative electrode structure 140 and LiNiMnCoO ₂ (NMC) of the positive electrode structure 120, but in some embodiments, the negative electrode structure 140 may also include lithium absorbing materials, such as silicon, tin, etc. Although the Li-ion battery structure 100 shown is a planar structure, the layer stack can also be rolled into a cylinder; in addition, other battery structures (such as square batteries, button-type batteries) can be formed.

In one embodiment, the separator 130 is a porous polymerized ion conductive polymer substrate. In one embodiment, the multi-polymer substrate is a multilayer polymer substrate. In some embodiments, the separator 130 is composed of any commercially available polymer microporous membrane (eg single or multilayer), such as Polypore (Celgard LLC., Charlotte, North Carolina, USA), Toray Tonen (battery separator; BSF), SK Energy (Lithium-ion battery separator; LiBS), Evonik Industries (SEPARION® ceramic separator), Asahi Kasei (Hipore ^TM polyolefin flattened film), DuPont (Energain®) and other products.

The electrolyte injected into the battery components 120, 130, 140 may include liquid/colloid or solid polymer, and may be different from each other. In some embodiments, the electrolyte mainly includes salts and a medium (for example, in a liquid electrolyte, the medium may refer to a solvent; in a gel electrolyte, the medium may be a polymer matrix). The salt may be a lithium salt. Lithium salts include, for example, LiPF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN(CF ₃ SO ₃ ) ₃ , LiBF ₆ and LiClO ₄ , BETTE electrolyte (available from 3M Corp. located in Minneapolis, Minnesota, USA) and the above composition . Examples of solvents include ethylene carbonate (EC), propylene carbonate (PC), EC/PC, 2-MeTHF (2-methyltetrahydrofuran)/EC/PC, EC/DMC (dimethyl carbonate), EC/DME (Dimethylethane), EC/DEC (diethyl carbonate), EC/EMC (ethyl methyl carbonate), EC/EMC/DMC/DEC, EC/EMC/DMC/DEC/PE, PC/DME and DME/PC. The polymer matrix includes, for example, PVDF (polyvinylidene fluoride), PVDF: THF (PVDF: tetrahydrofuran), PVDF: CTFE (PVDF: chlorotrifluoroethylene), PAN (polyacrylonitrile), and PEO (polyethylene oxide).

Figure 2 illustrates a process flow diagram according to the described embodiment and summarizes an embodiment of a method 200 for forming an electrode structure. In some embodiments, the electrode structure formed by the method 200 is the negative electrode structure 140 shown in FIG. 1.

In operation 210, a cement solution is formed. In some embodiments, the binder solution includes one or more polymers dissolved in a solvent system. In one embodiment, one or more polymers are selected from styrene butadiene rubber (SBR), polystyrene (PS), and the above-mentioned compositions. In one embodiment, the solvent system includes a hydrocarbon solvent, such as xylene, toluene, or the foregoing composition. In one embodiment, the binder solution includes styrene butadiene rubber (SBR) and polystyrene (PS) dissolved in xylene.

In one embodiment, the concentration of SBR in the binder solution is about 0.1% to about 5% by weight based on the total weight of the binder solution (for example, about 0.1% to about 1% by weight, about 0.2% to about 0.8% by weight). %, about 0.3% to about 0.7% by weight, about 0.4% to about 0.6% by weight, or about 0.5% to about 1% by weight). In one embodiment, the PS concentration in the binder solution is about 0.1% to about 5% by weight (for example, about 0.1% to about 1% by weight, about 0.2% to about 0.8% by weight) based on the total weight of the binder solution. %, about 0.3% to about 0.7% by weight, about 0.4% to about 0.6% by weight, or about 0.5% to about 1% by weight). In one embodiment, based on the total weight of the binder solution, the SBR concentration in the binder solution is about 0.5% by weight, and the PS concentration in the binder solution is about 0.5% by weight. In one embodiment, based on the total weight of the binder solution, the SBR concentration in the binder solution is about 0.1% to about 1% by weight, and the PS concentration in the binder solution is about 0.1% to about 1% by weight. In one embodiment, the total concentration of PS and SBR in the binder solution is not more than about 1% by weight based on the total weight of the binder solution.

In one embodiment, the viscosity of the adhesive solution at 20° C. is about 2.5 centipoise (cp) or more. In another embodiment, the viscosity of the adhesive solution at 20°C is about 3.6 centipoise (cp) or more. In another embodiment, the viscosity of the adhesive solution at 20° C. is about 4.8 centipoise (cp) or more. In another embodiment, the viscosity of the adhesive solution at 20°C is about 2.5 centipoise (cp) to about 4.8 cp (for example, about 2.5 cp to about 3.6 cp at 20°C; or about 3.6 cp to about 4.8 cp).

In operation 220, the stabilized lithium metal powder is added to the binder solution to form a binder suspension or slurry. In one embodiment, the stabilized lithium metal powder is coated with a thin lithium salt layer. Examples of lithium salts include lithium carbonate, lithium oxide, lithium hydroxide, lithium phosphate, or a combination of any two or more of the foregoing. In some embodiments, the coating on the stabilized lithium metal particles is about 10 nanometers (nm) to about 200 nm thick. In some embodiments, the particle size of the stabilized lithium metal particles is less than about 150 microns (μm). In some embodiments, the particle size of the stabilized lithium metal particles is about 125 μm, about 100 μm, about 75 μm, about 50 μm, about 30 μm, about 20 μm, about 10 μm, about 5 μm, about 1 μm. , About 100 nm or any range between any of the above two values, or less than any value. In some embodiments, the particle size of the stabilized lithium metal particles is about 5 μm to about 150 μm (for example, about 5 μm to about 50 μm or about 100 μm to about 150 μm).

In one embodiment, the stock of stabilized lithium metal particles is about 0.1% to about 5% by weight of the total weight of the binder suspension or slurry, and the binder solution is generally left as the remainder (for example, the stock is the binder About 95% to about 99% by weight of the total weight of the suspension or slurry). In one embodiment, the amount of stabilized lithium metal particles is about 0.5% to about 4% by weight of the binder suspension or slurry. The amount of stabilized lithium metal particles may be about 0.1% by weight, 0.2% by weight, 0.5% by weight, about 1% by weight, about 1.2% by weight, about 1.4% by weight, about 1.6% by weight of the total weight of the binder suspension or slurry. %, about 1.8% by weight, about 2% by weight, about 2.2% by weight, about 2.4% by weight, about 2.6% by weight, about 2.8% by weight, about 3% by weight, about 3.2% by weight, about 3.4% by weight, about 3.6% by weight %, about 3.8% by weight, about 4% by weight, about 4.2% by weight, about 4.4% by weight, about 4.6% by weight, about 4.8% by weight, about 5.0% by weight, or any range between any two of the foregoing.

In one embodiment, the inventory of the binder solution is about 95% to about 99.9% by weight of the total weight of the binder suspension or slurry. The inventory of the binder solution can be about 95.0% by weight, 95.2% by weight, 95.5% by weight, about 96% by weight, about 96.2% by weight, about 96.4% by weight, about 96.6% by weight of the total weight of the binder suspension or slurry. About 96.8% by weight, about 97% by weight, about 97.2% by weight, about 97.4% by weight, about 97.6% by weight, about 97.8% by weight, about 98% by weight, about 98.2% by weight, about 98.4% by weight, about 98.6% by weight, About 98.8% by weight, about 99.0% by weight, or any range between any of the above two values.

In one embodiment, based on the total weight of the binder solution, the total inventory of PS and SBR is 1%, and the remainder is solvent. Based on the total weight of the binder suspension or slurry, the inventory of stabilized lithium metal particles is about 0.5 Weight% to about 4% by weight, with the remainder being a binder solution.

In operation 230, a bonding agent suspension or slurry is deposited on the substrate to form a film on the surface of the substrate. In one embodiment, a doctor blade process, dip coating, slot die coating process, and/or gravure coating process are used to deposit the binder suspension or slurry. In some embodiments, the slurry is mixed to provide a homogeneous mixture. In some embodiments, the binder suspension or slurry is continuously mixed before being deposited on the substrate. In some embodiments, the distance between the deposition mechanism where the binder suspension or slurry is released and the surface of the substrate on which the slurry is to be deposited is greater than 100 μm (for example, about 100 μm to about 500 μm, about 100 μm to about 300 μm, or about 200 μm to about 400μm).

In operation 240, the film is exposed to a drying process. Exposing the film to the drying process can remove the binder solution and/or any remaining remaining in the deposition process What solvent. In one embodiment, the drying process can evaporate the hydrocarbon solvent from the electrode structure. The drying process may include, but is not limited to, a drying process such as an air drying process, for example, exposing the porous layer to heated nitrogen, an infrared drying process, or an annealing process.

In operation 250, the film is exposed to a pressure process to activate the SLMP. Not limited to theory, it is believed that the pressurization process can destroy the protective lithium salt coating on the SLMP and activate the SLMP. After the particles are deposited on the conductive substrate, physical pressing technology can be used to press the particles, such as a calendering process, to make the dense particles reach a predetermined net density while flattening the surface of the layer. Any pressurization technique suitable for fully activating SLMP can be used.

Depending on the situation, after the electrode structure is formed, the electrode structure is combined with the separator and the cathode structure to form a battery. A Li-ion battery having an electrode structure according to an embodiment of the present invention can be combined with a positive electrode structure, a separator, and a current collector to form a battery, such as the Li-ion battery structure 100 shown in Figure 1. The electrode structure can be integrated with other battery components in the same manufacturing facility used to manufacture the electrode structure, or the electrode structure can be transported and integrated elsewhere.

In one embodiment, the battery manufacturing process generally proceeds as follows: provide separators, negative electrode structures, and positive electrode structures; individually cut separators, negative electrode structures, and positive electrode structures into predetermined size sheets for use in batteries; add tabs To the positive and negative electrode structure slices; combine the positive and negative electrode structure slices and separators to form a battery cell; wind or stack the battery cells to form a predetermined battery cell structure; after winding or stacking, the battery pack The battery is put into the can, the can is evacuated, filled with electrolyte, and then sealed.

The aforementioned electrode structures mainly designed for high-energy rechargeable lithium batteries can be used in other battery systems.

Examples:

The following non-limiting examples are provided to further illustrate the embodiments. However, these examples are not intended to include everything and are not intended to limit the scope of the embodiments.

Material and electrode manufacturing

The graphite anode mixture includes graphite (CGP-G8 graphite powder, taken from ConocoPhillips), carbon black ("DENKA BLACK", taken from Denka Company Limited), and polyvinylidene fluoride (PVDF, taken from Kureha America, Inc.). The SiO anode includes carbon-coated SiO (taken from Hydro-Québec) and poly(9,9-dioctylco-co-co-methylbenzoate) (PFM, synthesized by the inventor). Stabilized Lithium Metal Powder (SLMP®) was obtained from FMC Corporation. The lithium nickel manganese cobalt oxide (LiNi _{1/3Mn1/3Co1/3} O ₂ ) cathode was taken from Umicore. N-Methyl-2-pyrrolidone (NMP) (anhydrous, 99.5%), chlorobenzene, toluene and xylene were obtained from Sigma-Aldrich®. Poly(styrene-butadiene copolymer) (SBR) was taken from Sigma-Aldrich®. Polystyrene (PS) with a molecular weight of 2,000,000 was taken from Alfa Aesar.

The anode slurry is composed of 89% by weight CGP-G8 graphite powder, 8% by weight PVDF and 3% by weight acetylene black (AB), and is homogenized with a Polytron® PT10-355 homogenizer before lamination. Next, the graphite slurry was coated with a Mitutoyo blade of a Yoshimitsu Seiki vacuum coater. The current collector is a 18 μm thick battery-grade copper sheet. The typical active material mass loading is 6.5 mg/cm². After the NMP is dried, the electrode is dried in a vacuum oven at 130°C for another 16 hours before loading the SLMP. The same mixing and coating procedure is applied to the SiO laminate. The SiO laminate is made of 95% by weight SiO powder and 5% PFM conductive adhesive in chlorobenzene. The typical SiO mass loading is 1.2 mg/cm². The cathode laminate used for CGP-G8 graphite is 85% by weight LiNi _{1/3Mn1/3Co1/3} O ₂ , 8% by weight PVDF and 7% by weight AB. The cathode laminate for SiO was made by Argonne National Laboratory with 90% by weight NCM-622, 5% by weight PVDF (Solef® 5130, from Solvay) and 5% by weight carbon black (TIMCAL SUPER C45 carbon black).

SLMP Coating procedure

The binder solution is made by dissolving SBR and PS in xylene in different weight ratios. Then SLMP was added and fully dispersed in the binder solution to form an SLMP suspension with a weight ratio of 0.5% (for graphite) and 2.0% (for SiO) of SLMP. Change the amount of SLMP in the solution to control the loading. Then, the SLMP suspension was coated on the anode laminate using the doctor blade method. The gap of the scraper can also be adjusted to control the SLMP loading on the surface of the laminate. After the xylene is dried, the SLMP-coated electrode is rolled with a roller press (EQ-MR 100A, from MTI Corporation) to activate the SLMP. The laminate is then stamped for battery assembly.

Battery assembly and testing

The BR2325 button battery was made (parts were taken from the National Research Council of Canada) to test the pre-lithiation effect of SLMP. The SLMP loaded battery was assembled in an argon-filled glove box with an oxygen mixing ratio of less than 0.2 ppm. Pressure activated SLMP-graphite and SLMP-SiO are used as anodes. The counter electrode of the half-cell is an 11/16" OD lithium metal disk (Li foil from FMC-Lithium Co.). The electrolyte used for the half-cell graphite and the full-cell is composed of ethyl carbonate (EC) with a volume ratio of 1:1 ) And a 1M LiPF ₆ solution of diethyl carbonate (DEC) (purchased from BASF). The electrolyte used for the SiO half-to-full battery consists of ethyl carbonate (EC) and diethyl carbonate in a weight ratio of 3:7 ( DEC) 1M LiPF ₆ solution and containing 30% by weight of fluoroethylene carbonate (FEC) (purchased from BASF). Celgard® 2400 separator was taken from Celgard®. Tested on 4000 series batteries taken from Maccor, Inc. Constant current cycle test is performed on the device. For graphite and SiO half-cells, the voltage operating range is 0.01-1.0 volts (V). Before cycling, the battery containing the pressurized activated SLMP is allowed to stand for a certain period of time (two days) ), to balance the prelithiation. In terms of the full battery, the area capacity ratio of the cathode and anode is 1:1. The battery capacity is calculated based on the cathode.

Material characterization

The JSM-7500F scanning electron microscope used in Lawrence Berkeley National Laboratory and Molecular Foundry National Center for Electron Microscopy (NCEM) to characterize the electrode surface topography. The viscosity was measured with a DV-E viscometer manufactured by Brookfield. The test is carried out at 23°C room temperature.

result

Solvents used in solution processing methods

In some embodiments of the present invention, the compatibility of the solvent and SLMP is important. According to previous reports, SLMP is incompatible with some polar solvents, such as 1-methyl-2-pyrrolidone (NMP). Only hydrocarbon solvents such as hexane, toluene and xylene are stable to lithium metal. As for the choice of binder for SLMP slurry, poly(styrene-butadiene copolymer) (SBR) has been used for SLMP operations. So first choose SBR as the binder of SLMP slurry. Both SBR and PS can be dissolved in toluene and xylene to form a homogeneous solution. The ability of the binder solution to maintain the uniformity of the SLMP suspension for a long time is very important. Therefore, a solvent with high viscosity is better. The viscosity of toluene and xylene are 0.55 cP and 0.61 cP at 25°C, respectively. This means that xylene should be more suitable for maintaining SLMP slurry than toluene. However, pure toluene and xylene are not viscous enough to keep SLMP dispersed in the slurry. Due to the extremely low density of SLMP and the low viscosity of the solution, SLMP particles tend to float on the surface of the solvent. In addition, after being deposited on the anode surface, since there is no polymer binder, the SLMP will fly off due to the lack of adhesion between the SLMP and the laminated surface after the solvent evaporates. Therefore, the polymer binder was introduced into the solution treatment method, and the influence of the polymer binder on the SLMP coating was further studied.

Used for SLMP Binder solvent concentration of suspension / Viscosity

The solution treatment method of incorporating polymer into the SLMP coating will greatly increase the viscosity of the adhesive solution. Therefore, it is proved that a well-dispersed SLMP suspension can maintain a uniform dispersion for a long operation time. The polymer is introduced as a binder to fix the SLMP on the anode surface after the solvent evaporates. SBR and PS are chosen as binders. SBR has strong cohesive ability, so it can provide good adhesion between SLMP and anode surface. Study the characteristics of polymer solutions with different SBR concentrations (0%, 0.5%, 1%, 3% and 5%) on SLMP coatings. The viscosities of 0.5%, 1%, 3% and 5% SBR solutions at 20°C were 1.02 cP, 2.52 cP, 15.00 cP and 36.90 cP, respectively. Dispersing the same amount of SLMP in each SBR solution can confirm the retention of the SLMP slurry by each binder solution. Take photos after the slurry is mixed and left to stand for different times (0 seconds, 30 seconds and 120 seconds). It is proved that adding a polymer binder can effectively increase the viscosity of the solution and keep the SLMP uniformly dispersed in the slurry. It was also confirmed that the higher the concentration of the polymer binder solution, the better the retention of SLMP dispersed in the slurry.

SEM was used to study the morphology and distribution of SLMP coatings with different SBR concentrations. Significant differences in different concentrations can be observed from low and high magnification images. In the coating with 0.5% SBR, very little SLMP coating on the anode surface can be observed. This is because the viscosity of 0.5% SBR solution is too low (1.02 cP), and the density difference between lithium and xylene is too large (the density of lithium is 0.534 g/cm ^ 3 and the density of xylene is 0.87 g/cm ^ 3). As a result, most of the SLMP floats on the surface of the coating suspension during the coating process, and is removed by the doctor blade during application. When the SBR concentration increases to 1%, the viscosity increases to 2.52 cP, SLMP can remain dispersed in the slurry for 120 seconds, and a uniform SLMP coating is achieved on the anode surface. When the SBR concentration was increased to 3% and 5%, the SLMP coating was uniform, but the amount of SLMP coated on the laminated surface did not increase much compared with the coating with 1% SBR solution. Therefore, it is found that the ability to maintain the SLMP slurry will increase with high viscosity. When the viscosity of the binder solution is greater than 2.5 cP, a uniform SLMP coating can be achieved. Therefore, the following discussion sets the binder concentration to 1%. Further efforts are made to achieve uniform coating and simple pressure activation. It can be adjusted slightly when using other polymer binders.

For efficient pressurization / Calendering activated binder species

When the polymer binder is introduced into the treatment method, re-evaluate the activation feasibility and efficacy of the activation process. From the SEM image of SLMP with 5% SBR binder, it can be observed that there is a polymer shell on the surface of SLMP. In contrast, no polymer shell was seen in the 1% binder solution, and very few shells were seen on the SLMP coated with 3% SBR. The question is whether the thin polymer shell will negatively affect the pressure activation process. Therefore, the SEM morphology of the SLMP coated anode before and after the electrolyte was studied, and the polymer binder concentration of 3% was used to confirm the role of the polymer shell.

It is proved that applying appropriate pressure to the SLMP coated anode will crush most of the Li ₂ CO ₃ coating of the SLMP. After immersing the press-activated SLMP coated anode in the electrolyte for 48 hours, the pre-lithiated anode can be observed again by SEM. All the powder SLMP disappeared. However, some unreacted SLMP particles were found through careful observation of high-magnification SEM images. Observing the oblate shape implies that the particles have been compressed, but the lithium does not directly contact the electrode, and the lithium does not react with the anode and electrolyte. Since SBR is known to have high elasticity, the shell cannot be effectively broken under pressure. The SBR shell on the surface of SLMP prevents electrical contact between the lithium core, anode and electrolyte, resulting in insufficient SLMP activation under pressure.

There are two ways to eliminate the inefficient activation caused by the polymer binder shell. First, when the binder concentration is low, it is less likely to form a complete shell. However, low binder concentration may cause other problems, such as uneven SLMP dispersion, poor retention, and poor attachment to the anode surface. Second, choose a polymer binder with less elasticity as an alternative application. So the introduction of polystyrene (PS). The conversion temperature (Tg) of PS is 95°C, and SBR is -65°C, which means that PS is more brittle and more easily broken than SBR, which helps the pressurization activation process. In addition, PS with high molecular weight can be obtained, so compared with the same concentration of SBR solution, a PS solution with higher viscosity can be obtained.

Three groups of binder solutions (1% by weight PS, 1% by weight SBR, 0.5% by weight PS and 0.5% by weight SBR) are used to enhance the composition of the binder and make it easier to activate under pressure. Obtained SEM images of SLMP loaded on the graphite surface before and after calendering and after 48 hours of immersion in electrolyte and using 1% PS, 1% SBR, 0.5% PS and 0.5% SBR binder solution. For the SLMP coating with 1% SBR and 0.5% PS and 0.5% SBR binder solution, a uniform SLMP coating can be observed. Calendering will crush the SLMP on the graphite surface, and when different binder solutions are used, the anode has a similar shape. After immersing the rolled electrode in the electrolyte for 48 hours, all the crushed SLMP particles disappeared from the SEM image. The SLMP coating with 1% PS solution, 0.5% PS and 0.5% SBR solution was observed with high magnification SEM and almost no residual SLMP was seen. Only two residual SLMPs were observed in the 1% SBR solution. This means that partial or full use of PS as a polymer binder is beneficial to achieve high-pressure activation efficiency.

With adhesive solution SLMP Uniformity of coating

In order to study the retention of the three binder solutions, 1% PS, 1% SBR, 0.5% PS and 0.5% SBR solutions were used to make SLMP slurry. The viscosity of the adhesive solution with 1% PS, 1% SBR, 0.5% PS and 0.5% SBR at 20°C is 4.83 cP, 2.52 cP and 3.60 cP, respectively. This further confirms that PS with high molecular weight can produce higher viscosity. Take photos of SLMP suspension at different times (0 seconds, 30 seconds and 120 seconds). It is observed that in all three solvents, SLMP is uniformly dispersed for more than 120 seconds. After 5 to 6 minutes, the SLMP slurry can be seen to start to phase separate. This means that the polymer binder composition can provide sufficient time and continuous coating process to process the homogeneously dispersed SLMP suspension.

Carry out the doctor blade method to coat SLMP in the adhesive solution (1% PS, 1% SBR, 0.5% PS and 0.5% SBR prepared in xylene). The photos of SLMP coated graphite anodes with different binder solutions are used to demonstrate the ability to achieve uniform SLMP coating and good SLMP attachment. Although three binder solutions are used, the retention of the SLMP slurry is comparable and the appearance of the SLMP coating is similar before the solvent evaporates. The SLMP coating with 1% PS binder solution showed poor adhesion to the electrode surface. After the solvent evaporates, most of the SLMP particles tend to float to the edge instead of attaching to the anode surface. However, using 1% SBR and 0.5% PS and 0.5% SBR binder solutions, after the solvent evaporates, a uniform SLMP coating can be achieved and the SLMP is well attached to the anode surface. Not limited to theory, it is believed that the reason for the difference is that the conversion temperature (Tg) of PS is 95°C and that of SBR is -65°C. The glass transition temperature is the temperature below which the polymer is in the glass phase and the polymer structure is rigid. Therefore, at room temperature (25°C), PS is in a fragile glass state and cannot be used as a soft glue; while SBR is in a soft and flexible rubber state, which can be used as a good adhesive to fix SLMP on the anode surface. It is believed that the high flexibility of the SBR chemical structure helps the SLMP and the SBR adhesive to bond well. In the case of 1% PS without SBR, it is believed that the poor attachment of SLMP is caused by the rigid PS structure. Based on this knowledge, the two polymers are combined to form a mixed binder solution. Flexible SBR helps to achieve good SLMP attachment, and rigid PS helps to achieve easier press activation. Therefore, the overall consideration is to achieve long-term maintenance of SLMP slurry, uniform SLMP coating, good SLMP adhesion and easy activation. It is believed that the best composition of the adhesive and solvent composition for the treatment method is 0.5% PS and 0.5% SBR adhesive preparation In xylene solution, excellent coating effect can be observed.

graphite /NMC Pre-lithiation of full battery

Two battery chemistries were used to demonstrate the pre-lithiation effect of coating SLMP using the solution processing method. The two battery chemistries include graphite/NMC full battery and high energy density SiO/NMC full battery. The pre-lithiation effect of SLMP on graphite/NMC full-cell and graphite half-cells is depicted in Figure 3A to Figure 3F. Figure 3A illustrates the voltage distribution of the first cycle of the graphite/NMC full battery with and without SLMP prelithiation. In the voltage region of less than 3.5V, the battery without SLMP pre-lithiation shows charge capacity, which is equivalent to graphite anode lithiation and SEI formation in the first cycle. As for the battery with SLMP pre-lithiation, before the cycle, SEI has been formed in the pre-lithiation process and the graphite has been partially lithiation, so the open circuit voltage starts from 3.5 V, and there is almost no display capacity when it is less than 3.5 V. During the formation of SEI, the lithium ion loss of the whole battery can be compensated by adding SLMP. The coulombic efficiency in the first cycle is increased to 87.8%. According to Figure 3B, this is higher than that of the graphite/NMC battery without SLMP prelithiation. 82.35%. In addition, the cycle stability of the graphite/NMC full battery can be greatly improved with the pre-lithiation of SLMP. This means that the irreversible lithium loss failure mechanism of the full battery can be partially compensated by adding extra lithium ions from SLMP.

The prelithiation of SLMP on the anode can also be observed from the voltage distribution of the graphite half-cell shown in Figure 3C. The 0.7-0.8 V voltage flat area in the half-cell without SLMP prelithiation indicates that the SEI is formed at the beginning of the lithiation process. As shown in Figure 3C, the initial voltage of the SLMP pre-lithiation half-cell has reached below 0.3 V, which further proves that SEI formation is achieved in the SLMP pre-lithiation process. The cycle performance of graphite and NMC half-cells are shown in Figure 3D and Figure 3F, respectively, and the voltage distribution of the NMC half-cell shown in Figure 3E is taken as a reference.

SiO/NMC Pre-lithiation of full battery

FIG. 4A is a voltage distribution diagram of a SiO/NMC full battery in the first cycle without and without SLMP according to one or more embodiments of the present invention. Fig. 4B is a cycle performance diagram of the first cycle of the SiO/NMC full battery without and with SLMP according to one or more embodiments of the present invention. SLMP prelithiation becomes critical in high energy density anodes (such as Si or SiO, etc.) because it has a first cycle Coulomb loss of up to 40%-50%. The pre-lithiation effect of SLMP can be confirmed by the SiO/NMC full battery coated by the solution processing method. The SiO anode is composed of SiO nanoparticles (95% by weight) with a conductive binder (PFM, 5% by weight). As shown in Figure 4B, the SLMP pre-lithiated full battery can be seen significantly improved. According to the treatment method, the first cycle CE increased from 56.78% (without SLMP prelithiation) to 88.12% (with SLMP prelithiation). This is because in the design of a full battery, the lithium ions of the cathode are accurately calculated to match the anode capacity, without too much lithium ions. The formation of SEI during the first few cycles will consume most of the excess lithium ions, and the long-term cycle capability will be impaired due to the loss of lithium ions. In addition, during the formation of SEI, the lithium ion consumption of the SiO anode is much greater than that of the graphite anode. Therefore, without SLMP pre-lithiation, the full battery capacity of SiO/NMC was initially only about 110 mAhg ^-1 , and after 100 cycles it decreased to about 80 mAhg ^-1 (based on the weight of the cathode). In the case of SLMP prelithiation, the SiO/NMC full battery maintains a reversible capacity of about 130 mAhg ^-1 after more than 100 cycles. Therefore, by coating SLMP on the anode of a full battery, the calculated amount of lithium ions can be added to the system and compensated for the loss of lithium ions during the formation of SEI. Accordingly, it can be seen that the cycle performance of the SiO/NMC full battery is significantly improved.

In summary, some embodiments of the present invention provide a simple solution treatment method to achieve a large area and uniform SLMP coating on the anode surface for pre-lithiation of lithium ion batteries. The binder solution can maintain uniform dispersion of the slurry for the coating process. In addition, by adding a polymer binder, SLMP can be fixed on the anode surface to facilitate transportation before activation. Considering the retention and coating performance, SLMP adhesion and easy activation, the best composition of the adhesive and solvent composition for the treatment method is 0.5% PS and 0.5% SBR. The adhesive is prepared in xylene solution, and it can get excellent Coating effect. The pre-lithiation effect of this method can be applied to graphite half-cells, graphite/NMC full-cells, SiO half-cells, and SiO/NMC full-cells. Compared with the corresponding batteries without SLMP pre-lithiation, the cycle performance will be improved and the first The second-cycle Coulombic efficiency is higher. The above results confirm that the method of the present invention has a positive effect and can be widely applied to different anode systems with different battery chemistries.

When introducing elements or exemplary aspects or embodiments of the present invention, the articles "a", "an", "this" and "this" are intended to mean one or more elements.

The terms "include", "include", and "have" are intended to be inclusive, and mean that in addition to the listed elements, additional elements may be included.

Unless otherwise stated, all amounts, ratios, ratios and other measured values are by weight. According to the practice of the present invention, unless otherwise indicated, all percentages represent weight percentages based on the total composition.

Although the above description is directed to the embodiments of the present invention, other and further embodiments of the present invention can be planned without departing from the basic scope of the present invention. Therefore, the scope of the present invention shall be subject to those defined by the attached patent scope.

100‧‧‧Lithium ion battery structure 110‧‧‧Positive current collector 120‧‧‧Positive electrode structure 130‧‧‧Separator 140‧‧‧Negative electrode structure 150‧‧‧Negative current collector 200‧‧‧Methods 210,220 , 230, 240, 250‧‧‧Operation

In order to make the above-mentioned summary features of the present invention more obvious and understandable, it can be described with reference to the embodiments, and some of the embodiments are illustrated in the accompanying drawings. However, it should be noted that the accompanying drawings only illustrate typical embodiments of the present invention, and therefore should not be regarded as limiting the scope of the present invention, because the present invention can accommodate other equivalent embodiments.

Figure 1 illustrates a cross-sectional view of an embodiment of a lithium ion battery structure having an electrode structure formed according to the embodiment; Figure 2 illustrates a flow chart of the manufacturing process according to the embodiment, and Summarize an embodiment of a method for forming an electrode structure; Figure 3A depicts a graph of the voltage distribution of the first cycle of a graphite/NMC full battery without and with SLMP according to one or more embodiments of the present invention; Figure 3B is a graph depicting the cycle performance of the first cycle of a graphite/NMC full battery without and with SLMP according to one or more embodiments of the present invention;

Figure 3C depicts a graph of voltage distribution during the first cycle of the graphite half-cell without and without SLMP according to one or more embodiments of the present invention;

The 3D diagram depicts the cycle performance diagram of the first cycle of the graphite half-cell with and without SLMP according to one or more embodiments of the present invention;

Fig. 3E depicts the voltage distribution diagram of the first cycle of the NMC half-cell without and with SLMP according to one or more embodiments of the present invention;

Figure 3F depicts a cycle performance diagram of the first cycle of an NMC half-cell without and without SLMP according to one or more embodiments of the present invention;

Fig. 4A depicts a voltage distribution diagram of the first cycle of a SiO/NMC full battery without and with SLMP according to one or more embodiments of the present invention; and

FIG. 4B depicts the cycle performance diagram of the first cycle of the SiO/NMC full battery without and with SLMP according to one or more embodiments of the present invention.

To facilitate understanding, the same component symbols are used as much as possible to represent similar components shared in each figure. It should be understood that the elements and characteristic structures of a certain embodiment can be beneficially incorporated into other embodiments, and will not be further detailed here.

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200‧‧‧Method

210, 220, 230, 240, 250‧‧‧operation

Claims (20)

A method of making an electrode structure, the method includes the following steps: forming a hydrocarbon solvent, a binder solution of styrene-butadiene rubber (SBR) and polystyrene (PS); adding stabilized lithium metal powder to the Bonding agent solution to form a slurry; depositing a thin film of the slurry on a substrate; and exposing the thin film and the substrate to a drying process to form the electrode structure. The method according to claim 1, wherein the step of depositing the thin film includes a slot die coating process. The method according to claim 1, further comprising the following steps: exposing the thin film on the substrate to a calendering process to activate the stabilized lithium metal powder. The method according to claim 1, wherein the substrate is a graphite anode. The method according to claim 1, wherein the substrate is a silicon monoxide (SiO) anode. The method according to claim 1, wherein the hydrocarbon solvent is xylene. The method according to claim 1, wherein the adhesive solution A viscosity of about 2.5 centipoise (cp) or more at 20°C. The method according to claim 1, wherein an SBR concentration in the cement solution is about 0.1% to about 5% by weight based on a total weight of the cement solution. The method according to claim 8, wherein the SBR concentration in the cement solution is about 0.1% to about 1% by weight based on the total weight of the cement solution. The method according to claim 9, wherein a PS concentration in the cement solution is about 0.1% to about 5% by weight based on the total weight of the cement solution. The method of claim 10, wherein the PS concentration in the cement solution is about 0.1% by weight to about 1% by weight based on the total weight of the cement solution. The method of claim 1, wherein based on a total weight of the adhesive solution, an SBR concentration in the adhesive solution is about 0.5% by weight, and a PS concentration in the adhesive solution is about 0.5% by weight . The method according to claim 1, wherein the stabilized lithium metal powder particles are coated with Li ₂ CO ₃ . The method of claim 1, wherein the drying process will evaporate the hydrocarbon solvent from the electrode structure. A method of forming a battery, including combining such as claim 1 The electrode structure and a positive electrode structure, a first current collector contacting the positive electrode structure, a second current collector contacting the electrode structure, and a separator arranged between the positive electrode structure and the electrode structure. A method for forming a stabilized lithium metal powder (SLMP) suspension. The method includes the following steps: dissolving styrene-butadiene rubber (SBR) and polystyrene (PS) in xylene to form a binder Solution; and adding SLMP to the binder solution to form the SLMP suspension. The method according to claim 16, wherein a viscosity of the adhesive solution is about 2.5 centipoise (cp) or more. The method according to claim 16, wherein an SBR concentration in the cement solution is about 0.1% to about 1% by weight based on a total weight of the cement solution. The method according to claim 18, wherein a PS concentration in the cement solution is about 0.1% to about 1% by weight based on the total weight of the cement solution. The method of claim 16, wherein based on a total weight of the cement solution, an SBR concentration in the cement solution is about 0.5% by weight, and a PS concentration in the cement solution is about 0.5% by weight .

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